Mathematical models for feedback and feedforward compressors are developed in this paper. The
author analyzes the transfer functions for a linear-output rms detector in conjunction with a linearly
controlled VCA (linear-domain compressor) and a logarithmic-output rms detector in conjunction
with an exponentially controlled VCA (log-domain compressor). It is shown that both transfer
functions are equivalent. Comparisons between feedback and feedforward configurations are
discussed to optimize their attributes for specific applications.

Protection of audio intellectual properties has become a subject of great concern in the digital age of
audio. Audio watermarking techniques are compared and discussed relative to the need for
robustness and adaptability to the program material in which the watermark is embedded, and its
transparency within the program content. The authors propose a content-adaptive multiple-echo
hopping technique to embed the watermark into audio signals, which is claimed to be superior to
many of the current systems. It is anticipated that reliable watermarking will become even more
important as digital techniques expand.

A Csound implementation for synthesizing Woodstock gamelan tones has been developed. This
synthesized model produces tones that are very close to the original instrument's tones, according to
listening tests. It can also produce attractive related timbres with simple changes to the model
parameters.

The advantages of virtual acoustic (3-D audio) displays to achieve spatial separation for stereo
headphone users have been investigated by the author. The technique separates multiple
communication channels by placing each sound source at a unique virtual audio position, thereby
simulating and exploiting the "cocktail party" effect. This approach increases the intelligibility of
audio signals against noise in an "unmasking" process.